1. Field of the Invention
The invention relates to a magnetic tape drive system for passing a thin flexible magnetic tape along a plurality of magnetic heads and comprising:
(A) a "flip-over" reversible magnetic tape cassette, which is adapted to be supported on a magnetic tape cassette recording and/or playback apparatus (hereinafter called a cassette apparatus) in a first and in turned over or reversed second position, in either of these positions the magnetic tape being disposed to permit cooperation with the magnetic heads. Such a cassette has first and second adjacent reel hubs which are rotatable about parallel axes of rotation, each hub having a substantially tubular reel winding member which has an at least substantially cylindrical inner wall (as used herein "cylindrical" is to be understood as meaning circular cylindrical) and two annular end walls which are disposed in planes at some axial distance from each other perpendicular to the axis of rotation, as well as a disc-shaped centering and drive member midway between and parallel to the two end walls of the reel winding member and provided with parts which define a central centering aperture as well as at least one drive aperture at some radial distance from the centering aperture; first and second plane-parallel main walls which axially enclose the two reel hubs with play, each provided with a first aperture coaxial with the first reel hub and a second aperture coaxial with the second reel hub; and a length of magnetic tape having a first end connection to the first reel hub and having a second end connected to the second reel hub, so as to enable it to be wound back and forth between the reels, with a straight tape portion along the front of the magnetic tape cassette.
(B) a cassette apparatus having a frame a drive arrangement comprising first and second drive spindles which are rotatable about parallel axes of rotation, each provided with a centering in with a free end adapted to cooperate with the centering apertures in the reel hubs of the magnetic tape cassette; each drive spindle having at least one drive pin with a free end, disposed at some radial distance from the centering pin, resiliently depressable in a direction parallel to the axis of rotation of the drive spindle, and adapted to cooperate with a drive aperture in the reel hubs of the magnetic tape cassettes during operation; and cassette supporting means connected to the frame for cooperation, in the cassette first or second position, with the first or the second main wall respectively and thus supporting the magnetic tape cassette on the drive arrangement in an operating position in which the two reel hubs cooperate with the centering pins and the drive pins of the two drive spindles.
2. Description of the Prior Art
Such a magnetic tape drive system is known from U.S. Pat. 3,027,110. In this magnetic tape drive system a plurality of drive apertures are formed in the disc-shaped centering and drive member of each reel hub at equal radial distances from the axis of rotation of the reel hub and at equal distances from each other. If two separate winding motors for the two reel hubs were used, the spindles of the winding motors could also be used as centering pins for centering the reel hubs. The height positions of the reels in the magnetic tape cassette are determined by the location of the cassette on the cassette supporting means.
The known magnetic tape drive system is intended for recording and/or reproducing audio signals on magnetic tape. For video applications, where signals of substantially larger bandwidth than in audio applications should be recorded and reproduced, such a magnetic tape drive system is less suitable. In the currently used magnetic video tape recorders which have been designed for the consumer market the signals are written on the magnetic tape with the aid of rotary video heads as obliquely oriented elongate and closely adjoining tracks. The oblique tracks are approximately 18 to 23 microns wide at a length of approximately 100 mm, while in some magnetic tape recorders, employing two magnetic video heads with different azimuth alignments the tracks directly adjoin each other without intermediate spacing. In order to ensure that with such magnetic tape drive systems a video cassette which has been recorded on one specific video recorder can be played back on another video recorder without loss of quality, a high accuracy of the tape transport and the tape guidance is essential, so that variations in the stretch of the magnetic tape and thus variations in the tension in the magnetic tape are minimized. In addition, the one video recorder should be capable of reading the tracks which have been written on the magnetic tape by another video recorder, and time errors should also be avoided because of their adverse effect on the picture quality. In view of the stringent compatibility requirements thus imposed undefined frictional forces should not be exerted on the magnetic tape reels, while other sources of tape tension variations should be eliminated as far as possible.
Conventional video recorders employ several servo systems so as to obtain an accurate tape transport speed and minimal tape tension variations. As an example, the speed of rotation of the capstan is automatically controlled by means of one servo system, while other servo systems drive the rotary magnetic heads, the magnetic head control and the drive spindles. As a result of the variations in tension which occur in the magnetic tape, frictional forces which act an the magnetic tape reels represent errors for the last-mentioned servo systems and also for the other servo systems.